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--- en:iot-open:remotelab:sut:generalpurpose2:b6 [2020/04/28 19:20] – created pczekalski
+++ en:iot-open:remotelab:sut:generalpurpose2:b6 [2020/07/20 12:00] (current) – external edit 127.0.0.1
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+==== B6: Presenting air pressure on the LCD ====
+In this scenario, you will present absolute air pressure reading, on the LCD screen.
+=== Target group ===
+Beginners
+=== Prerequisites ===
+You need to know, how to print and position text on the LCD display.
+Use LCD I2C library to control it:
+<code c>
+#include <LiquidCrystal_I2C.h>
+</code>
+The air pressure sensor is Bosch BMP280 sensor, connected to the I2C bus, shared with LCD display.
+To read data you may use a dedicated library (libraries):
+<code c>
+#include <Adafruit_Sensor.h>
+#include <Adafruit_BMP280.h>
+</code>
+=== Scenario ===
+Once you initialise sensor and LCD display, read sensor data (air pressure) and then display them in the loop. Give each loop execution some 5-10s delay.
+<note warning>Do not try to read air pressure too frequent. Once every 5s is quite enough both for information and safe enough to not let your readings race with the communication protocol.</note>
+The first line of the LCD should display: "//Air pressure is://"\\
+The second line should provide temperature within the "//NNNN.NN hPa//" form, in hPa.\\
+<note>Note - your readings are in Pa (not hPa) so you're supposed to divide them by 100 before presenting on the screen!</note>
+You will use ''sprintf'' function to format string and convert from float to string.
+=== Result ===
+You should be able to see air pressure readings on the LCD display using the video stream. Some fluctuations are natural.\\
+<note important>If the fan connected to the air chamber is on, air pressure measured may be higher than the ambient air pressure observed and higher disturbances will be observed.</note>
+=== Start ===
+There are no special steps to be performed.
+=== Steps ===
+== Step 1 ==
+Include LCD and sensor driver libraries:
+<code c>
+#include <LiquidCrystal_I2C.h>
+#include <Adafruit_Sensor.h>
+#include <Adafruit_BMP280.h>
+</code>
+== Step 2 ==
+Instantiate software controler component for the LCD display:
+<code c>
+LiquidCrystal_I2C lcd(0x3F,20,4);   // set the LCD address to 0x3F for nodes 1 through 5, 8 and 9 for a 20 chars and 4 line display
+//LiquidCrystal_I2C lcd(0x27,20,4); // for nodes 10 and 11 only!
+Adafruit_BMP280 bmp;
+</code>
+== Step 3 ==
+Declare a buffer for ''sprintf'' function and floating point value (single precision is enough) for storing last air pressure reading:
+<code c>
+char buffer [11];
+float pres;
+</code>
+== Step 4 ==
+Initialize LCD and BMP sensors:
+<code c>
+...
+  lcd.init(D2,D1);     // initialize the lcd
+  lcd.backlight();
+  lcd.home();
+...
+  if(!bmp.begin(0x76))
+  {
+    lcd.print("Bosch Sensor Error!");
+    delay(1000);
+  };
+  lcd.home();
+  bmp.setSampling(Adafruit_BMP280::MODE_NORMAL,     /* Operating Mode. */
+                  Adafruit_BMP280::SAMPLING_X2,     /* Temp. oversampling */
+                  Adafruit_BMP280::SAMPLING_X16,    /* Pressure oversampling */
+                  Adafruit_BMP280::FILTER_X16,      /* Filtering. */
+                  Adafruit_BMP280::STANDBY_MS_500); /* Standby time. */
+...
+</code>
+The BMP sensor address is 0x76 and, if not initialised, display error on the LCD screen.
+== Step 5 ==
+Read in the loop:
+<code c>
+...
+  pres = bmp.readPressure()/100;
+...
+</code>
+''bmp.readPressure()'' function returns air pressure in //Pa//. You must convert it //hPa//, dividing by 100.
+To convert float into the string with formatting use ''sprintf'' function:
+<code c>
+...
+  sprintf(buffer,"%4.2f hPa",pres);
+...
+  delay(5000);
+...
+</code>
+<note tip>''sprintf'' uses number of wildcards that are rendered with data. Refer to the c/c++ documentation on ''sprintf''. Here <code c>%4.2f</code> means: having float number render it to string using four digits before decimal point and two after it. Air pressure readings should be somewhere between 890 and 1060 hPa.\\
+''delay(time)'' is measured in milliseconds.</note>
+=== Result validation ===
+Observe air pressure readings on the LCD. Note - small oscillations are natural - you can implement moving average (i.e. of 10 subsequent reads, FIFO model) to "flatten" readings.